The invention pertains to a chromium-containing cemented tungsten carbide body such as a cutting insert. While applicants contemplate other applications, these cutting inserts are suitable for the milling of various metals including without limitation titanium and titanium alloys, steel alloys, and cast iron alloys.
Titanium metal and many of its alloys (e.g., Tixe2x80x946Alxe2x80x942Zrxe2x80x942Mo and Tixe2x80x946Alxe2x80x944V) possess a high strength-weight ratio at high temperatures, as well as exceptional corrosion resistance. These very desirable properties allow titanium and its alloys to have particular application to the aerospace industry for use in airframes and engine components. Titanium and titanium alloys also have application for use in medical components, steam turbine blades, superconductors, missiles, submarine hulls, chemical processing equipment and other products where corrosion resistance is a concern.
Titanium and titanium alloy possess physical properties that make them difficult to mill. These special challenges require the careful selection of cutting inserts used in the milling of titanium and titanium alloys.
Among the metalcutting processes, milling places the most demands on the cutting insert. The cutting insert repeatedly enters, cuts and then exits the workpiece, and thus sustains repeated mechanical and thermal shocks. Thermal shocks and mechanical shocks can each result in microchipping of the cutting edge of the cutting insert.
Titanium and titanium alloys have a low thermal conductivity so as to worsen the ability to transfer heat into the workpiece. The temperature at the interface of the chip and the cutting insert may be about 1100 degrees Centigrade. At an interface temperature of greater than about 500 degrees Centigrade, titanium and titanium alloys are chemically reactive with some cutting insert materials, as well as the nitrogen and oxygen in the air. The combination of the high temperatures and the high chemical reactivity results in diffusion of elements from the cutting insert into the chips to cause cratering of the cutting insert.
The cutting insert-chip interface may also be under high pressure. For example, these pressures can be in the range of 1.38 to 2.07 gigapascal. These high pressures at the cutting edge may lead to the deformation and fracture of the cutting edge.
U.S. Pat. No. 5,750,247 to Bryant et al., which is hereby incorporated by references herein, further describes milling operations. U.S. Pat. No. 5,984,593 to Bryant, which is hereby incorporated by reference herein, further describes the milling of titanium and titanium alloys.
While earlier coated cutting insert have satisfactory performance, it would be desirable to provide a coated cutting insert that has improved ability to be able to withstand the mechanical shocks and thermal shocks of a milling operation. It would also be desirable to provide a coated cutting insert that is able to better resist cratering, deformation and fracturing due to the high temperatures and high pressures at the cutting insert-chip interface. Although these coated cutting inserts may have application to metalcutting applications in general, they would have specific application to the milling of titanium and its alloys, steel alloys, and cast iron alloys.
In one form, the invention is a coated cutting insert that comprises a tungsten carbide-based substrate that has a rake surface and a flank surface, the rake surface and the flank surface intersect to form a substrate cutting edge. The substrate comprises between about 10.4 weight percent and about 12.7 weight percent cobalt, between about 0.2 weight percent and about 1.2 weight percent chromium, tungsten and carbon. There is a coating on the substrate. Preferably, chromium is present at about 0.3 to 0.8 weight percent of the substrate.
In another form thereof the invention is a coated cutting insert that comprises a tungsten carbide-based substrate that has a rake surface and a flank surface, the rake surface and the flank surface intersect to form a cutting edge. The substrate consists essentially of greater than about 10.5 weight percent cobalt, greater than about 0.4 weight percent chromium, and less than about 89.1 weight percent tungsten and carbon. There is a coating on the substrate.
In still another form thereof, the invention is a tungsten carbide-based cutting insert substrate that comprises a rake surface and a flank surface wherein the rake surface and the flank surface intersect to form a substrate cutting edge. The tungsten carbide-based substrate comprises between about 10.4 weight percent and about 12.7 weight percent cobalt, between about 0.2 weight percent and about 1.2 weight percent chromium.